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20 Cards in this Set

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Ediacaran Fossils
Bilaterians not yet recognized

Molecular clock analyses suggest bilaterian groups should be present

Fossils from China may be bilaterian embryos
Cambrian Explosion
545 million years ago, worldwide

Nearly all of the major groups of bilaterians occur by the Cambrian

Hard-bodied animals suddenly appear

Possibly correlated with increase in oxygen

May be related to origin of Hox gene clusters
Burgess Shale
Middle Cambrian (505 million years), 40 million years after the initial explosion

Canadian Rockies, similar faunas found in a few other places

Soft tissues are preserved (a Lagerstatte), so soft-bodied animals are present
Origin of Tetrapods
Tetrapods are land vertebrates (amphibians, reptiles, birds, mammals)

Closest living relatives are lungfish and coelacanths

Tetrapods have a variety of distinctive adaptations
Tetrapod Adaptations
Ear drum transmits sounds from the air; hearing apparatus modified from gill support

Distinctive limbs support the animal on land; shoulder and pelvis well developed, shoulder not attached to skull

Gills and fin rays are lost
most primitive tetrapod
Acanthostega
Bird Origins
Birds are highly specialized:

Toothless skull with many air sacs
Clavicle modified into furcula
Hand bones fused, only three fingers
Pelvis modified with pubis rotated back
No tail
Three-toed foot
Feathers
Archaeopteryx
Discovered 2 years after Darwin’s “Origin of Species” published

Feathers and furcula, but reptilian skeleton - teeth, hand not fused, long tail, pelvis intermediate

Very similar to theropod dinosaurs (e.g., Velociraptor)
Theropods and Birds
In every part of the skeleton theropods show a progression of features grouping them with birds

The closest relatives are dromaeosaurs such as Velociraptor and troodontids
Clavicle bone in all of these organisms
In birds, the clavicles (collar bone) form a single bone, the furcula ("wishbone"). Crocodylians lack clavicles, primitive dinosaurs have separate clavicles, and in the theropods closest to birds a furcula is present. The furcula of Archaeopteryx is unusually robust, and some theropod dinosaurs have the same kind of furcula.

The "boomerang" shaped furcula of oviraptor thereopods is nearly identical to the furcula of Archaeopteryx.
Pelvis of these organisms
In the pelvis of birds the pubis is rotated backwards. In Archaeopteryx
the pubis is only partly rotated, and in the theropods closest to birds it is
also partly rotated.
Finger Homology and the Origin of Birds
Comparative anatomy of theropods indicates bird fingers are 1-2-3

Development of the hand in living birds indicates it is 2-3-4
Hands of theropods
The hands of archosaurs, showing the reduction of the fourth
and fifth fingers in theropod dinosaurs and birds
Frame Shift?
The development of the bird fingers might be explained by a shift in the genes controlling the positions of the digits

The position of the digits is moved, to 2-3-4, but their shapes are similar to 1-2-3
Whales
Molecular evidence indicates that whales evolved from within artiodactyls, and may be closely related to hippos (the “whippo” hypothesis)

Recent fossils show stages in the transition from terrestrial mammals to aquatic whales
Whale Adaptations (4)
Hind limbs are lost

Ear is specialized for echolocation

Teeth simplified or lost (in baleen whales)

Nose moved to back of head (blow hole)
closest fossil relatives of whales
A mesonychid (Sinonyx)
Whale evolution (3)
Ambulocetans, 50 million year old amphibious
Whale from Pakistan

Rhodocetus, primitive whale with echo-locating
ear and blow hole, well developed pelvis

Basilisaurus, a primitive fossil whale (note
vestigial pelvis)
Human Origins
Closest living relatives are chimpanzees

Fossil record of humans begins 6-7 million years ago

Adaptations include erect posture, enlarged brain, flattening of face, reduced incisors and canines
Origin of Modern Humans (2 Hypotheses)
Out of Africa - Modern humans evolved from Homo erectus in Africa and migrated outward

Multi-regional hypothesis - Modern humans evolved independently from Homo erectus in Asia, Africa, Australia and Europe